1. Technical Field
The present invention relates in general to the quality of disks in a hard disk drive, and in particular to an improving the chamfer quality of the edge surfaces of data storage disks in hard disk drives.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
The only other moving part within a typical HDD is the actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions (air bearing design) on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
The outer radial edges of hard disks used for magnetic storage of data have historically caused contamination problems. The sharp corner defining the boundary between the data storage surface of the disk and the disk edge is subject to chipping and cracking with subsequent release of the particles onto the disk surface. Additionally, the edge corner can cut into the plastic holding cassette, again releasing contaminants and debris that may find their way onto the data storage surface of the disk.
For these reasons, a common approach has been to chamfer or bevel the edge corners of a disk in an attempt to mitigate this problem. While helpful, the chamfering process, particularly on glass substrates, often leaves the resulting surface with defects and scribe marks. Thus, the chamfer surface may act as a source of debris. Indeed, microscopic analysis of chamfer surfaces reveal mechanical marks, chips, and abrasions that generate additional contamination. Thus, an improved apparatus and method for fabricating hard disks is needed.
One embodiment of the present invention is an apparatus and method that uses a non-contact, non-mechanical means for smoothing and polishing the as-cut chamfer surface at the edge of the disk. Since glass disk substrates strongly absorb infrared radiation, a carbon dioxide (CO2) laser provides high quality polishing and smoothing action for the mechanically cut chamfer surfaces of glass disk substrates. The silicon-oxygen bond that is abundantly available in silicate glasses of the type used for storage disks, such as magnetic data storage disks, strongly absorbs CO2 laser radiation in the 9 to 11 xcexcm wavelength regime.
Applying laser radiation to the glass surface at the correct power density for an appropriate duration causes transient melting and resolidification. Due to surface tension effects, the glass resolidifies to produce a surface that is significantly smoother than it was before irradiation. If scratches or abrasive marks are present on the glass surface prior to irradiation, the irradiation process xe2x80x9cpolishes outxe2x80x9d these defects as long as they are not too deep. At a wavelength of 10 xcexcm, the penetration depth of the radiation into the glass is approximately 1 xcexcm. Therefore, scratches and defects of this order of magnitude are eliminated. The quality of the resulting modified chamfer surface is far superior to the original mechanically ground and polished surface.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.